Japan’s expanding defense partnerships signal strategic shift

Felix Kim

The Indo-Pacific security landscape is being reshaped through expanding defense partnerships that emphasize interoperability, shared norms and a commitment to regional stability. Japan is leading the way by building a flexible, multilayered architecture of bilateral, trilateral and multilateral cooperation designed to deter coercion and strengthen maritime domain awareness.

Tokyo’s One Cooperative Effort Among Nations (OCEAN) framework, unveiled in 2025, reflects a broader initiative to promote deeper security coordination regionwide.

Japan’s layered cooperation allows the nation to “support partners and shape the regional environment,” said Dr. Jeffrey Hornung, an expert on Japan’s defense policy at the Rand Corp., a United States-based think tank. Under this approach, Japan strengthens partner capacity via its Official Security Assistance program, defense equipment transfers, joint training and strategic dialogues.

Ties with Association of Southeast Asian Nations (ASEAN) members have become central to this approach, with initiatives such as the Japan-ASEAN Ministerial Initiative for Enhanced Defense Cooperation (JASMINE) aligning Tokyo’s efforts with regional priorities under ASEAN’s Outlook on the Indo-Pacific.

The Philippines has emerged as a key partner. Since becoming the first OSA recipient in 2023, Manila has received coastal radar systems through Japan’s program, with additional surveillance and maritime assets planned through 2026. The Japan-Philippines Reciprocal Access Agreement, which entered into force in September 2025, has enabled more streamlined joint exercises, including Doshin-Bayanihan a month later.

“We now consider this whole area as one area where we could cooperate in several aspects,” Gen. Romeo Brawner Jr., the Armed Forces of the Philippines chief of staff, told FORUM in March 2026, referring to the first island chain. The string of archipelagoes, which includes Japan and the Philippines, is a vital line of defense for the U.S. and its Allies and Partners.

Under JASMINE, the Japan Self-Defense Forces have conducted training focusing on “practical defense cooperation between Japan and ASEAN,” including maritime security and cybersecurity. The efforts enhance deterrence, Hornung told FORUM.

Trilateral drills with Australia and the U.S., such as Bushido Guardian, offer Tokyo operational insights that “bilateral U.S.-Japan engagements alone may not,” Hornung said.

In Southeast Asia, Japan also co-chairs an ASEAN group on maritime security with the Philippines, demonstrating Tokyo’s commitment to regional ownership, Hornung said, noting that Japan is considered “a trusted partner.”

Tokyo’s defense engagement increasingly is backed by industrial cooperation and legal reform. Australia’s $6.5 billion contract with Japan’s Mitsubishi Heavy Industries in 2025 for 11 frigates represents Tokyo’s most significant defense manufacturing collaboration. Other joint projects include the Global Combat Air Program with Italy and the United Kingdom to deploy a next-generation fighter jet by 2035, and the Glide Phase Interceptor system being developed with the U.S. to counter hypersonic missiles.

Through such defense cooperation, Tokyo promotes principles such as international law and freedom of navigation amid regional tensions, Hornung said.

Felix Kim is a FORUM contributor reporting from Seoul, South Korea.